Firing control means



Oct. 11, 1966 G. c. JUILFS ETAL.

FIRING CONTROL MEANS 2 Sheets-Sheet 1 Filed Sept. 22. l965 INVENTORS. GEORGE C. Jum s AND FRANK W. PueH,

ATTO R N EYS- Oct. 11, 1966 G. c. JUILFS ETAL 3,278,105

FIRING CONTROL MEANS Filed Sept. 22, 1965 2 Sheets-Sheet 2 o s A 4 9 5'5 61 "y 5 7 5 4e 57 A y 0 I2 7 62 8 & 9 1; 19 52 /0 67 56/576 45 \gv'f 48 INVENTORS. GEORGE QJUILFS AND BY FRANK W. PUGH,

Fig.5 W)%Z.IAJ at ATTORNEYS.

United States Patent 3,278,105 FIRING CONTROL MEANS George C. Juilfs and Frank W. Pugh, Cincinnati, Ohio, assignors to Senco Products, Inc., Cincinnati, Ohio, a corporation of Ohio Filed Sept. 22, 1965, Ser. No. 489,142 5 Claims. (Cl. 227--130) This invention relates to fastener applying devices, and more particularly to an improved firing control and safety means for pneumatically operated fastener applying devices.

In a conventional, pneumatic fastener applying device, compressed air from a suitable source of supply is admitted into a working cylinder to drive a piston or working member and its associated driver in a power stroke. A plurality of fasteners from a magazine or other source of supply are successively fed into position to be driven by the driver on its working stroke. Control of the admission of air into the working cylinder of the tool is achieved by a suitable firing control means, which, especially in the case of the larger tools, will take the form of a remote valve. As is well known in the art, the remote valve serves to control the opening and closing of a firing valve at the head of the working cylinder. The remote valve or other firing control means is normally actuated means of a manual trigger under the control of the operator.

With particular but exemplary reference to stapling and nailing devices, technology is continually developing to permit the driving of larger and larger fasteners, this of course requiring more and more driving power in the tool itself. In addition, manufacturers and operators have become increasingly conscious of the possibility and desirability of increasing the speed of operation of such devices.

These two factors, along with other conditions, have created a severe safety problem, and made it extremely desirable to provide a simple and positive safety structure. In other words, it is obvious that a fastener applying device which develops enough power to drive a two inch fastener into hard wood, can certainly drive that fastener a considerable distance through the air with the resultant possibility of injury.

Similarly, in response to the demand for increased speed of operation, the prior art has developed fastener applying devices in which the firing control means is actuated by means of a touch-fire member. This touch-fire member extends slightly beyond the nose piece of the tool, so that simply placing the nose piece of the tool against a work piece actuates the firing control means, and fires the tool. This construction permits an operator to drive a plurality of fasteners simply by placing the fastener applying device against the work piece in the proper position. But, should the operator inadvertently permit the nose piece of the tool to come in contact with his body, a coworker, or anything other than the proper work piece, the tool will fire, with the resultant possibility of injury.

The prior art has also developed a number of safety devices which are in some respects similar to the above described touch-fire control. That is, the safety device includes a member projecting slightly beyond the nose piece of the fastener applying device. The firing of the tool is controlled by a manually actuated trigger, which is so designed that it cannot be moved or actuated until, by placing the tool against a work piece, the safety member has been actuated. A safety such as the one just described is entirely adequate from the standpoint of safety, but has been found in practice to materially cut down the rate of operation of the tool, inasmuch as this 3,278,105 Patented Oct. 11, 1966 arrangement requires a series of operations which must be carried out in sequence in order to fire the tool.

Accordingly, it is a general object of this invention to provide a simple and positive safety mechanism which will not affect the maximum speed of operation of the tool with a skilled operator.

More specifically, it is a very important object of this invention to provide a fastener applying device which may be operated either by placing the nose piece of the device against the work piece, or by means of a manual trigger.

Still a further object of the invention is the provision of a firing control means requiring concurrent actuation of two separate and independent actuating members, one of the actuating members being controlled manually by the operator of the device, while the other of the actuating members is controlled 'by placing the tool against a work piece.

Another object of this invention is to provide such a firing control means wherein the two independent actuating members must concurrently be in the firing position to cause the tool to drive a fastener, and wherein operation of the actuating members may be effected in any order.

Keeping the above objects in mind along with such other advantages that Will become apparent as this specification proceeds, the invention will be described in terms of a pneumatic stapler; but it is to be understood that the following specific description is exemplary only, and that the invention is equally applicable to any and all fastener applying devices.

Reference will be made from time to time to the accompanying drawings, wherein similar reference numerals have been used to indicate like parts throughout the several views.

In the drawings:

FIGURE 1 is a side elevational view, partly in section, showing the firing control means of this invention as applied to a pneumatic stapler;

FIGURE '2 is a cross-sectional view taken along the line 2-2 of FIGURE 1;

FIGURE 3 is a cross-sectional view similar to a portion of FIGURE 1, showing the firing control means of this invention in one position which may be realized during the course of operation;

FIGURE 4 is a cross-sectional view showing the same elements seen in FIGURE 3, but showing a second position which may be realized during operation of the device; and

FIGURE 5 is a cross-sectional view similar to FIG- URES 3 and 4 showing the firing control means in still another position.

Briefly, the practice of this invention contemplates a remote firing control means, which, upon actuation, controls the opening and closing of a firing valve and hence the admission of compressed air into the working cylinder of the tool. Operation of this firing control means is controlled by two separate and independent actuating members, both of which must be in the fully actuated or firing position to cause the tool to drive a fastener. One of the aforesaid actuating members is responsive to a manual trigger, and the other actuating member is responsive to a touch fire member extending a slight distance beyond the nose piece of the tool. These actuating members each include a control cam, these cams together coacting with a firing element as described in more detail hereinafter to provide four operating positions. These are (l) a normal position wherein neither of the actuating members has been operated, (2) a first safe position wherein only the manually actuated trigger has been operated, (3) a second safe position wherein only the touch fire member has been operated, and (4) a firing 3 position wherein both the actuating members have been operated.

The fastener applying device to which the firing control means of this invention has been applied in the drawings is one wherein the tool completes only one-half of an operating cycle upon operation of the firing control means. That is, a charge of compressed air is admitted into the working cylinder, driving the piston to its lowermost position, which of course will drive a fastener into an appropriate work piece. The working piston remains in this down position, until the firing control means is returned to its starting position. The coacting cam surfaces and firing element described briefly above are so designed that after the tool has been fired by concurrent operation of both actuating members, release of either actuating members will be operative to cause the tool to complete its cycle, and make it ready for a subsequent cycle.

Referring now particularly to FIGURE 1, the fastener applying device to which the firing control means of this invention is applied includes the housing 1 surrounding the walls of the working cylinder, and closed at its upper end by means of the cap 2 having the downwardly projecting, hollow central post 2a.

The cap 2 may be secured to the housing 1 in any conventional manner, and is provided with the resilient sealing means 3 to prevent the loss of fluid under pressure.

Slidably received about the post 2:: and within the housing 1 is the firing valve piston 5, which is sealed against the post 2a by means of the O-ring 4, and sealed against the housing 1 by means of the O-ring 6. The lower portion of the firing valve piston 5 is provided with the annular, resilient valve member 7, which is adapted to seat against the firing valve seat 12, as will be described in more detail hereinafter. The lower portion of the post 2a is provided with the exhaust valve washer 8, which, in the position shown in FIGURE 5, is in sealing engagement with the O-ring 9 on the inside of the piston 5, thereby closing off the exhaust passages through the post 2a. Between the exhaust valve washer 8 and the post 2a. is the O-ring 10, which is held in a compressed position by the spacer collar 11, the firing valve seat 12, and the spring clip 13. This firing valve arrangement is described in greater detail in US. Patent No. 3,170,487, entitled Springless Firing Valve.

Received within and spaced from the housing 1 is the liner 18, forming the working cylinder for the tool. Slidable within the liner 18 is the working piston provided with an annular groove containing the O-ring 16, maintaining a seal between the edge of the piston 15 and sleeve 18. Secured to the lower surface of the piston 15 as for example by the pin 14 is the fastener driver 17. It will of course be understood that the nose piece of the tool is provided with a drive track (not shown) within which the fastener drive 17 reciprocates.

The liner 18 carries at its upper edge a groove holding the O-ring 19, which effects a seal between the upper surface of the cylinder wall and the firing valve seat 12. The lower portion of the liner 18 is provided with resilient sealing means 20, effecting a seal between the outer surface of the liner 1'8 and the inner surface of the housing 1, thereby forming and maintaining two distinct air reservoirs within the housing, as will be described subsequently.

At the bottom of the working cylinder is provided the resilient piston stop 22, which defines the lower most position of the piston 15 at the end of its working stroke. Spaced above the top surface of the piston stop 22 by substantially the thickness of the piston 15 are a plurality of ports 23 in the liner 18. These ports 23 open into an annular groove in the liner 18, which carries the O-ring 21. This O-ring in effect forms a one way valve; when the piston 15 is in its lower most position, the compressed fluid driving the piston passes through the ports 23 and tends to force the O-ring 21 outwardly, thereby escaping into the air return reservoir 64, until the pressure in the reservoir 64 substantially balances the pressure within the 6,, working cylinder, at which time the O-ring 21 will contract to its original position, closing the ports 23. These elements constitute the piston return system described in detail in US. Patent No. 2,983,922 entitled Portable Stapler With Pneumatic Drive and Return.

The magazine 26 is located immediately behind the nose piece 25 of the tool, and is adapted to carry a plurality of fasteners 27, urged by the spring follower 28 into the drive track (not shown) in a position to be driven by the driver 17.

The elements thus far described are entirely conventional, but it will be helpful to consider the operation of the device in general before proceeding to a discussion of the firing control means of this invention. In the position shown in FIGURE 1, compressed air at equal pressure is acting on both the upper surface 5a and the lower surface 5b of the firing valve piston 5. Due to the greater efiective area of the surface 5a, the firing valve piston is forced to its down or closed position. By means of the firing control means described hereinafter, the compressed air acting on the surface 5a is exhausted to atmosphere, thereby quickly reducing the pressure applied to this surface. The compressed air acting on the surface 5b then becomes sufficient to force the piston to its upper most position (shown in FIGURE 5) wherein the resilient valve member 7 is lifted off the firing valve seat 12, permitting the compressed air to rush into the driving cylinder, moving the working piston 15 downwardly, driving a fastener 27 in the process.

When the piston 15 reaches its lower most position, a portion of the compressed air driving the piston passes through the ports 23 into the chamber 64, where it is stored until the piston is to be returned.

Release of the firing control means serves to reintroduce compressed air to the space above the firing valve piston 5 where it acts on the surface 5a, once again forcing the piston downwardly until ultimately, it returns to the position shown in FIGURE 1. In this position, it will be seen that the exhaust valve washer 8 is out of engagement with the O-ring 9, thereby permitting the compressed air in the working cylinder to pass upwardly, around the exhaust valve washer 8, through the passage 57, and out the vent 58 to atmosphere. This reduction in air pressure on the top of the piston 15 permits the compressed air within the storage chamber 64 to act through ports 55 and the relieved area 24, to force the piston to its upper most position, so that the cycle may be repeated.

The firing control means of this invention includes the three tubular stacked sections 42, 47, and 49, formed as shown in the drawings. The lower most section, section 42, is provided with a recess and houses the actuating members 40 and 41, the opposed faces of which are formed into cam surfaces having the portions 40a and 40b, and 41a and 41b respectively. The actuating members each include a rod 38 and 39 respectively, extending through the base of the lower section 42 of the firing control means, whereby the actuating members 40 and 41 respectively may be operated independently and in any order by a trigger and a touch fire member, as briefly out lined earlier in this application.

The three sections 42, 47, and 49 may be assembled with the various components to be described shortly, and with the O-rings 43, 46, 50, and 51, and placed in the housing 1. The entire assembly will then be held in place by the cap 2.

The touch fire member 30 is essentially rectangular in cross section, and adapted to surround the nose piece 25 of the tool. In its normal or starting position, it extends a short distance beyond the end of the nose piece as is clearly shown in FIGURE 1. Suitably secured to each side of the touch fire member 30 are the upwardly extending curved arms 31. The upper ends of the arms 31 are joined by means of the pin 32, which passes through the bushings 33 which are free to slide in the slots 33a in the tool housing 1, and through the torch fire trigger 35,

the entire assembly being held in place by the spring clip 34.

The manually actuated trigger 36 is pivotally secured in the housing 1 of the stapler by means of the pin '37. As seen in FIGURE 2, the manually actuated trigger 36 is provided with an opening to receive the touch fire trigger 35.

It will be noted that the touch fire trigger 35 includes a downwardly extending leg 35a, which rests against the manual trigger pivot pin 37. It will therefore be apparent that as the touch fire member 3% is moved vertically with respect to the nose piece 25, the arms 31 will also be moved vertically and through the pin 32, will move the touch fire trigger 35 vertically. Vertical movement of the touch fire trigger 35 will, through the actuating rod 39, move the actuating member 41 upwardly against the resistance of the spring 45 to the position shown in FIG URE 4.

Separately and independently of movement of the touch fire member, pivotal motion of the trigger 36 about its pin 37 serves to move the rod 38 and actuating member 40 from the position shown in FIGURE 1 to the position shown in FIGURE 3, against the resistance of another spring Disposed between the opposed cam surfaces of the ac tuating members 4% and 41 is the firing element 44. In the embodiment shown, the firing element is a small, round ball, but in some cases, can be a short rod. The inter-action between the opposed cam surfaces 40a, 4% and 41a, 41b, and the firing element 44 will be described in more detail hereinafter.

The middle and upper sections of the firing control means, 47 and 49 respectively, house the valve member 48. The valve member 48 includes on its lower end a stem portion 43a extending into the lower most section 42, in a position to be contacted by the firing element 44. The valve member 48 is also provided near its lower end with the enlarged portion carrying the sealing O-ring 52,. Substantially centrally of the valve member 48 is a somewhat smaller O-ring 53, adapted, upon vertical movement of the valve member, to come into sealing engagement with the inner surface of the bore in the upper section 49 of the firing control means. The upper most end of the valve element 43 is provided with the O-ring 54, which in the normal position is in engagement with the inner surface of the bore in the section 49, and which, upon vertical movement of the valve member 43, will move into the relieved portion 63 at the upper end of the top section 49 of the firing control means.

The central section 47 of the firing control means is provided with a plurality of apertures 6t, in communication with a suitable supply of compressed air under pressure. The air under pressure thus enters the aperture 61, and in the normal position of the valve element 48, by passes the O-ring 53, entering the upper most section 49 of the firing control means. This upper section 49 is provided with a plurality of apertures 63 in communication with the passageway 59 formed in the housing 1 of the fastener applying device, and communicating therethrough with the space above the top of the firing valve piston 5.

The compressed air which has by passed the O-ring 53 into the upper section of the firing control means 49, is then free to pass through the ports 60, the passageway 59, and into the space above the firing valve piston, wherein pressure is exerted on the surface 5a, forcing the firing valve piston closed as described earlier in the specification.

A comparison of FIGURES 1, 3, 4 and 5 will clearly and graphically illustrate the important features and preferred design of the cam surfaces of the actuating memhers 40 and 41. Each of these cam surfaces includes a relieved portion 40a and 41a respectively, and a by pass portion 40b and 411) respectively. The shoulders 40c and 41c respectively, joining the by pass and relieved portions acts as a carnrning surface, as will now be described.

In FIGURE 1, the various components are shown in the normal or starting position. It will be observed that both the actuating members 40 and 41 are at their lower most or inoperative positions, the firing element 44 is resting on the carnrning surfaces 40c and 410, the valve element 48 is in its lower most position, and the firing valve piston 5 is in its lower most or closed position.

FIGURES 3 and 4 respectively illustrate a first safe position wherein only the manually actuated trigger 36 has been operated, and a second safe position wherein only the touch fire member 30 has been actuated. In FIGURE 3, it will be seen that the actuating member 41 remains in its lower most position, while the actuating member 40, under the influence of the trigger 36, has been moved to the upper most or firing position. As the actuating member 40 moves upwardly, the firing element 44 moves to the left, and is received between the by pass portion 41b of the actuating member 41 and the relieved portion 40a of the actuating member 40.

At this time, it should be pointed out that the enlarged portion of the valve element 48 containing the O-ring 52 serves a rather important function. By virtue of this enlarged portion, compressed air entering the ports 61 will tend to force the valve member 48 to its lower most position, and will retain it there against any upward pressure exerted by the firing element 44 due to movement of the actuating member 40 or 41.

In FIGURE 4, the positions of the actuating members 40 and 41 have been reversed; that is, by movement of the touch fire member 30, through the touch fire trigger 35, the actuating member 41 has been moved to its firing position, and the firing element 44 now is received between the by pass portion 40b of the actuating member 40 and the relieved portion 41a of the actuating member 41. Once again, the valve element 48 remains in its lower mos-t position.

Starting for example from the position shown in FIG- URE 3, wherein the manually actuated trigger 36 has been moved to the firing position, the tool will be caused to fire by placing the nose piece 25 against a Work piece, there-by moving the touch fire member 30, the touch fire trigger 35, the actuating member 41, and the firing element 44 to the position shown in FIGURE 5. It will be apparent that as the actuating member 41 moves to the position shown in FIGURE 5, the camming surface or shoulder 41c moves the firing element 44 upwardly against the stem 48a of the valve element 48, thereby overcoming the air pressure exerted on the enlarged end of the valve element and moving it to the position shown in FIGURE 5. In this position, it will be seen that the O- ring 53 is in sealing engagement with the bore of the upper section 49 of the firing control means. At the same time, the O-ring 54 has moved into the relieved portion 63 in the upper most end of the section 49 of the firing control means. The compressed air above the top surface of the firing valve piston 5 is then free to pass through the passage 49, the ports 60, around the Oring 54, into the relieved portion 63, and to atmosphere via the exhaust passage 63a. As briefly described earlier, this reduction in air pressure acting on the surface 5b of the firing valve piston to raise the piston to the position shown in FIGURE 5, thereby admitting compressed air into the working cylinder of the device, forcing the working piston 15 downwardly to drive a fastener into a Work piece.

Referring now again to FIGURE 1, the piston will continue this downward stroke until it is arrested by the piston stop 22, at which time a portion of the compressed air driving the piston will pass through the port 23 into the air return reservoir 64. The various components will remain in this position, so long as both the manual trigger 36 and the touch fire member 30 remain in the firing position.

However, as soon as either of these elements (the manual trigger 36 or the touch fire member are returned to the inoperative or safe position, the actuating member 40 or 41 associated with the trigger or touch fire member respectively will return to the safe position under the bias of spring 45. Air pressure acting on the large end of the valve element 48 will then force this element downwardly, in conjunction with spring and movement of the actuating member 40 or 41, will move the firing element 44 into either the position shown in FIGURE 3 or 4. At this time, the O-ring 54 returns to scaling engagement with the bore of the upper section 49 of the firing control means, thereby sealing off the exhaust passage 63a, and the O-ring 53 comes out of engagement with the bore of the section 49 of the firing control means, permitting compressed air to once again act on the upper surface 5a of the firing valve piston 5. As noted before, air pressure on the surface 5a will be operative to effect closing of the firing valve by moving the firing valve piston 5 to the position shown in FIGURE 1.

At this time, it will be seen that the working cylinder of the device is in communication with atmosphere by the ports 56 in the firing valve seat 12, around the exhaust valve Washer 8, through the passages 57 and 58. As the air pressure above the working piston 15 is exhausted, the air in the reservoir 64, acting through the ports and the relieved portion 24 around the periphery of the piston stop 22, serves to return the working piston to its upper most position.

Repeat cycles may then be carried out in the same manner described above.

Briefly reviewing the essential features of the firing control means of this invention, it includes two separate and independent actuating members. One of these actuating members is responsive to motion of a manual trigger, and the other of these actuating members is responsive to the position of the fastener applying device with respect to a work piece, that is, the touch fire member. In order to fire the tool, both of these actuating members must be moved from the normal position to the firing position. The order of movement of the actuating members is totally immaterial. That is, the tool may be placed against the work piece and the trigger then pulled to fire the tool, or the trigger may be held depressed, and the tool placed against the work piece to drive a fastener.

In this particular tool, the concurrent positioning of both the actuating members in the firing position will cause the tool to complete only half of an operative cycle, the working piston being driven to its lower most position. It is a further advantage of the firing control means of this invention that release of either of the actuating members, either the manual trigger, or the touch fire member, will cause the fastener applying device to complete its cycle and to be ready to begin the next cycle.

In other words, the tool can be operated in a conventional manner, by the operator placing it against the work piece and then pulling the trigger to drive a fastener where desired. Once the tool is against the work piece, it can be moved t-herealong, wit-h every depression of the trigger serving to drive a fastener. On the other hand, the trigger may be held in the depressed or firing position, and the tool will then fire simply by placing the nose piece against a work piece.

Numerous modifications may be made in this invention without departing from its scope and spirit. Hence, no limitations are intended except insofar as set forth in the following claims.

The embodiment of the invention in which an exclusive propertly or privilege is claimed are defined as follows.

We claim:

ll. In a fastener applying device including a working member, a fastener driver associated with said working member, means for driving said working member, and means for successively feeding a plurality of fasteners into position to be driven by said driver, the improved firing control means comprising:

(a) means for controlling the delivery of driving power to said working member;

(b) trigger responsive actuating means movable from an inoperative position to a firing position;

(c) work piece responsive actuating means movable from an inoperative position to a firing position;

(d) a firing element movable from a safe position to a firing position, said means for controlling the admission of driving power to said Working member being operatively associated with said firing element; and

(6) means including a pair of opposed cam surfaces, one of said cam surfaces being operatively connected to said trigger responsive actuating means and the other of said cam surfaces being operatively connected to said work piece responsive actuating means,

for moving said firing element to said firing position only when both said trigger responsive and said work piece responsive actuating means are moved to their respective firing positions, said means permitting said firing element to return to said safe position when one of said actuating means is returned to its inoperative position.

2. The improved firing control means according to claim 1 wherein said opposed cam surfaces each include a by pass portion, and a relieved portion, said firing element being normally disposed between said by pass portions, and upon movement of one of said actuating means to said firing position, movable to a position between said by pass portion of one of said cam surfaces and the relieved portion of the other of said cam surfaces.

3. The improved firing control means according to claim 2 wherein said firing element comprises a ball.

4. In a pneumatic fastener applying device including a working cylinder, a working piston reciprocable in said cylinder, a fastener driver associated with said working piston, and means for successively feeding a plurality of fasteners into a position to be driven by said driver, the improved firing control means comprising:

(a) at least two actuating members, said members being independently movable from an inoperative position to a firing position;

(b) a firing element movable from a safe position to a firing position;

(c) means comprising opposing cam surfaces associated respectively with said actuating members whereby said firing element is moved to said firing position only when both said actuating members are moved to said firing position; and

(d) means for controlling the delivery of compressed fi-uld to said working cylinder, said last named means being responsive to movement of said firing element from said safe position to said firing position.

5. The improved firing control means according to claim 4 wherein each said cam surface includes a by pass portion, and a relieved portion.

No references cited.

GRANVILLE Y. CUSTER, JR., Primary Examiner. 

1. IN A FASTENER APPLYING DEVICE INCLUDING A WORKING MEMBER, A FASTENER DRIVER ASSOCIATED WITH SAID WORKING MEMBER, MEANS FOR DRIVING SAID WORKING MEMBER, AND MEANS FOR SUCCESSIVELY FEEDING A PLURALITY OF FASTENERS INTO POSITION TO BE DRIVEN BY SAID DRIVER, THE IMPROVED FIRING CONTROL MEANS COMPRISING: (A) MEANS FOR CONTROLLING THE DELIVERY OF DRIVING POWER TO SAID WORKING MEMBER; (B) TRIGGER RESPONSIVE ACTUATING MEANS MOVABLE FROM AN INOPERATIVE POSITION TO A FIRING POSITION; (C) WORK PIECE RESPONSIVE ACTUATING MEANS MOVABLE FROM AN INOPERATIVE POSITION TO A FIRING POSITION; (D) A FIRING ELEMENT MOVABLE FROM A SAFE POSITION TO A FIRING POSITION, SAID MEANS FOR WORKING MEMBER MISSION OF DRIVING POWER TO SAID WORKING MEMBER BEING OPERATIVELY ASSOCIATED WITH SAID FIRING ELEMENT; AND (E) MEANS INCLUDING A PAIR OF OPPOSED CAM SURFACES, ONE OF SAID CAM SURFACES BEING OPERATIVELY CONNECTED TO SAID TRIGGER RESPONSIVE ACTUATING MEANS AND THE OTHER OF SAID CAM SURFACES BEING OPERATIVELY CONNECTED TO SAID WORK PIECE RESPONSIVE ACTUATING MEANS, FOR MOVING SAID FIRING ELEMENT TO SAID FIRING POSITION ONLY WHEN BOTH SAID TRIGGER RESPONSIVE AND SAID WORK PIECE RESPONSIVE ACTUATING MEANS ARE MOVED TO THEIR RESPECTIVE FIRING POSITIONS, SAID MEANS PERMITTING SAID FIRING ELEMENT TO RETURN TO SAID SAFE POSITION WHEN ONE OF SAID ACTUATING MEANS IS RETURNED TO ITS INOPERATIVE POSITION. 